Communications systems and datacenters are required to handle massive data at ever increasing speeds and ever decreasing costs. To meet these demands, optical fibers and optical ICs (such as, a photonic integrated circuit (PIC) or integrated optical circuit) are used together with high speed electronic ICs. A PIC is a device that integrates multiple photonic functions (similar to an electronic IC or RF IC). PICs are typically fabricated using indium phosphide or silicon oxide (SiO2), which allows for the integration of various optically active and passive functions on the same circuit.
The coupling of PICs to optical fibers is not as well advanced as the integration and/or coupling of electronic ICs. Specifically, the challenges facing optical connections are different and much more complex than connecting electronic ICs to, for example, a printed circuit board (PCB). Some difficulties are inherent in wavelength, signal losses, assembly tolerance, and polarization characteristics of optical packaging.
Existing solutions utilize various techniques for connecting optical fibers to PICs. One technique suggests using various types of butt connections to the edge and surface fiber connections a PIC. The butt of a fiber can be connected to a planar waveguide at the edge of a PIC. This technique is efficient only if the cross sectional of the propagating mode of the fiber and the waveguide areas of the fiber core and the waveguide are of similar size. In most cases, this technique suffers from poor assembly tolerance.
An improved technique suggests laying a section of fiber on top of the surface of the PIC where the end of the fiber has been cut at an angle to form an angled tip. The angled tip has a flat surface which reflects a light beam down to a waveguide grating coupler disposed on the integrated circuit. The light beam is reflected off the reflective surface of the angled tip by total internal reflection. The waveguide grating coupler is designed to accept the slightly diverging light beam from the reflective surface of the angled tip of the fiber. The light beam can also propagate through the fiber to a chip coupler in the opposite direction, up from the substrate through the waveguide grating and into an optical fiber after bouncing off the reflective surface of the angled tip. This technique further requires coating on the exterior of the reflective surface with epoxy.
Among others, all of the above-noted techniques require precise alignment and active positioning of the optical fiber to the PIC. As such, current techniques suffer from poor and very tight alignment tolerance to gain an efficient connectivity. For example, a misalignment between an optical fiber and a PIC of 1-2 microns (μm) would result in a signal loss of about 3 db. Furthermore, the alignment is now performed with expensive equipment or labor intensive assembly solutions. As a result, a mass production of PICs and/or optical couplers is not feasible.
It would therefore be advantageous to provide a fiber-to-chip optical coupling solution that would overcome the deficiencies of the existing solutions.